This invention relates to the field of RF modulators and more specifically to phase-shift-keyed (PSK) modulators.
Phase-shift-keyed digital data transmitters of the type which utilize a premodulation filter for reducing sideband splatter have a problem which is introduced because of the use of the premodulation filter. The problem is that during data transitions the amplitude of the RF carrier will decrease to zero as the phase of the carrier changes from positive to negative and back from negative to positive. This change in carrier amplitude when operated upon by a highly nonlinear class "C" power amplifier, of the type used in RF transmitters, creates amplitude holes in the modulated output carrier. These holes contribute to sideband splatter, which splatter negates the advantages of using a premodulation filter. A phase vector rotation, between positive and negative phases, wherein the amplitude of the phase vector remains substantially constant, would eliminate the amplitude holes and accompanying sideband splatter.